Semiconductor photocatalysis is considered one of the most promising technologies for water purification from toxic organic dyes. However, to reliably evaluate the possibility of using a given material as a photocatalyst, it is crucial to investigate not only the photocatalytic activity but also its affinity towards various dyes and reusability. In this work, we studied the adsorptive/photocatalytic properties of hollow-spherical raspberry-like SnO₂ and its SnO₂/SnS₂ heterostructures that were obtained via a chemical conversion method using three different concentrations of a sulfide precursor (thioacetamide). The adsorptive/photocatalytic properties of the samples towards cationic rhodamine B (RhB) and anionic indigo carmine (IC) were analyzed using uncommon wall zeta potential measurements, hydrodynamic diameter studies, and adsorption/photodecomposition tests. Moreover, after conducting cyclic experiments, we investigated the (micro)structural changes of the reused photocatalysts by scanning electron microscopy and Fourier-transform infrared spectroscopy. The obtained results revealed that the sensitization of SnO₂ resulted not only in the significantly enhanced photocatalytic performance of the heterostructures, but also completely changed their affinity towards dyes. Furthermore, despite the seemingly best photocatalytic performance, the sample with the highest SnS₂ content was unstable due to its (micro)structure. This work demonstrates that dye adsorption/desorption processes may overlap the results of cyclic photodecomposition kinetics.

SnO₂@SnS₂ multi-core–shell heterostructures were synthesised via chemical conversion of mesoporous raspberry-like SnO₂ nanocrystals. In the syntheses, different concentrations of a sulphide precursor (thioacetamide) were applied. The samples were analysed using scanning and high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results revealed the presence of surface defects (Sn²⁺, oxygen vacancies) on the raspberry-like surface, which play a crucial role in the chemical conversion reaction. With an increasing amount of thioacetamide, additional redox reactions occurred in the system (Sn⁴⁺/Sn²⁺, S²⁻/S⁰). The highest precursor concentration led to the microstructural disintegration and phase composition change. GRAPHICAL ABSTRACT IMPACT STATEMENT This paper demonstrates the role of defects on the formation of SnO₂@SnS₂ multi-core–shell heterostructures in mesoporous SnO₂ nanomaterials.

This work aims to demonstrate that the Fe₂O₃ nanocrystals’ adsorptive and photocatalytic properties can be adjusted by exposing the crystal facets that are functionalized. To this end, cube- and disc-like structures were synthesized using a metal ion-mediated hydrothermal route. Thereafter, some of the samples were annealed at 500 °C for 3 h. Our paper combines the experimental part with theoretical calculations of the obtained materials’ band edge positions. The results reveal that—aside from hematite—the as-synthesized discs also contain γ-FeOOH and β-Fe₂O₃ phases, which transform into α-Fe₂O₃ during annealing. The hydrodynamic diameter, zeta potential, and adsorption kinetics measurements show that the cube-like samples exhibit the highest affinity for cationic, whereas the discs have an affinity for anionic dye. Measurements of the wall zeta potential also reveal that annealing the discs modifies their surface state and ability to adsorb molecules. Photocatalytic tests show that the as-synthesized powders have better photocatalytic performance toward methylene blue decomposition than the annealed ones. The observed small changes in the concentration of the MO during illumination result from the energy band structure of the cube-like crystal orientation.